1. Field of the Invention
The present invention relates to system architecture, apparatus, and method for processing substrates in a clean environment, such as silicon wafers for semiconductor, solar cells, and other applications. The clean environment may be in vacuum or atmospheric pressure. The system can also be used with other substrates, such as glass for LCD and solar applications, stainless steel for thin film solar applications, etc.
2. Description of the Related Art
The photovoltaic (PV) solar cell industry can be roughly divided into two segments: thin film-based and silicon-wafer based PV cells. With the recent surge in demand for solar panels, various systems are currently being developed to enable high output manufacturing of various types of solar cells, both in silicon wafer and thin film manifestations.
State of the art systems for fabrication of semiconductor wafers generally utilize a mainframe about which several processing chambers are mounted. The mainframe is maintained in vacuum and houses a robotic arm. The arm moves individual wafers in and out of each processing chamber and out of the mainframe via a loadlock. The same architecture has been employed for fabrication of panels for flat panel display, albeit the mainframe and processing chambers are much larger for flat panel display substrates. Recently, such flat panel fabrication systems have been modified for fabrication of thin film solar cells, albeit with limited success. Another system being developed for thin film is a roll-to-roll system, wherein flexible substrate is provided from one roll, passed through the fabrication system, and collected on the other side into a spooling roll.
Another format for system architecture is the linear transport system. For thin film, these systems generally move large glass substrates on rollers in a linear fashion, entering the system from one end as clear glass and exiting the system on the other end as a fabricated solar cell. On the other hand, for silicon based fabrication, the linear system moves trays, upon which multiple silicon wafers are placed. The tray moves from chamber to chamber in a linear fashion, such that in each chamber many silicon wafers are processes concurrently on a single tray e.g., 64 substrates of 125 mm by 125 mm each. The trays enter from one side of the system and exit on the other side, and then need to be brought back to the entry side, e.g., using a transport system positioned under the series of fabrication chambers.
One of the advantages of the mainframe architecture is that if one chamber malfunctions or needs to be shut down, the system can continue to operate using the remaining chambers. Additionally, the system is modular, such that the user may run the system with any number of processing chambers according to its throughput requirements or other considerations. Conversely, in a linear architecture when one of the chambers is down, the entire system is shut down and cannot be used. Also, linear system is not modular, in that the number of processing chambers cannot be easily changed once the system is set up.
One of the advantages of a linear system is that it can process substrates at high throughput. That is, substrates move directly from one processing chamber to the next, without handling overhead of the mainframe robot between processing. Conversely, in a mainframe architecture, every time a process is completed in one chamber, the substrate must be picked up by the robotic arm and moved to another chamber, which adds transport overhead and reduces throughput. Also, for systems that move wafers without a tray, breakage of a wafer can cause a shut down of the entire system for clean up and recovery. Systems that use trays may avoid this issue if the tray can hold the fragmented wafer and carry the fragments out of the system.
As the demand for solar cell fabrication system continues to increase, there is a need for an architecture which can take advantage of the throughput of linear system, but also provide the flexibility of mainframe architecture.